Automatic control device for electronic flash

ABSTRACT

A DEVICE FOR AUTOMATIC CONTROL OF THE QUANTITY OF LIGHT FROM AN ELECTRONIC FLASH, BY COMPARING THE BRIGHTNESS OF A PHOTOGRAPHIC OBJECT WITH THE QUANTITY OF LIGHT REQUIRED FOR PARTICULAR PHOTGRAPHING CONDITINS INCLUDING THE DEGREE OF LENS APERTURE SELECTED AND THE SENSITIVITY OF THE FILM USED. THE BRIGHTNESS OF THE PHOTOGRAPHIC OBJECT IS MEASURED AS THE SUM OF THE NETURAL LIGHT BRIGHTNESS AND THE BRIGHTNESS DUE TO ELECTRONIC FLASH, AND AS SOON AS THE SUM BRIGHTNESS THUS MEASURED REACHES THE REQUIRED QUANTITY OF LIGHT, A STOP SIGNAL IS GIVEN. THEREBY, THE ELECTRONIC FLASH IS CONTROLLED, AND AT THE SAME TIME SIGNAL IS GIVEN FOR THE SUFFICIENT BRIGHTNESS OF THE PHOTOGRAPHIC OBJECT.

May 28, 1974 TQMQJ] MURATA E'I'AL Re. 28,025

AUTOMATIC CONTROL DEVICE FOR ELECTRONIC FLASH Original Filed April 18,1968 ll Sheets-Sheet 1 F IG I PHOTOELECTRIC FROM ELECTRONIC A I C.

FLASH Ps MPLIFIER INTEGRATOP LIGHT COM PARATOR ADDER PHOTOELECTRICSHUTTER SPEED ELEMENT FOR SETTING DETECTING NATURAL LIGHT Po I ALARMCIRCUIT ELECTRONIC I I FLASH swn'cume CIRCUIT START TRIGGER lNVF/VTURSTOMOJ/ MURATA 540,40 IAMAO/IA May 28, 1974 TOMOJI MURATA ETAL Re. 28,025

AUTOHATIC CONTROL DEVICE FOR ELECTRONIC FLASH Original Filed April 18,1968 11 Sheets-Sheet 2 FIG'.2

SWITCH CIRCUIT START TRIGGER H l "Ce L E2 0 TRIGGER i r TO ouTPuT CIR TS WINDING 0F BLOCKING SCRZ TRANSFORMER Tl I/VVE/VTORS TOMOJ/ All/R472154040 7441/10/64 By H i-F E' y 1974 TOMOJI MURATA ErAL Re. 28,025

AUTOMATIC CONTROL DEVICE FOR ELECTRONIC FLASH Original Filed April 18,1968 ll Sheets-Sheet 3 RQ/iy} K5 T r K45 i m+| 5i,'r Rag: ]K4j1,m

TO COMPARATOR INTEGRATOR FIG 5 NEI K;- 4 K+F2 To COMPARATOR RM i RIB? 4RlslE //VVE/V 70/?5 TOMOJ/ MU/PA 72! 54040 YAMAO/(A [WW Z 4 May 28. 1974TQMQJI MURATA ETAL Re. 28,025

AUTOMATIC CONTROL DEVICE FOR ELECTRONIC FLASH Original Filed April 18,1968 ll Sheets-Sheet 4 FIG 6 INTEGRATOR COMHARATOR ADDER A B H P F A 4FILM SENSITIVITY E g i i AND LENS APERTURE I o SETTING L P F 0.0 SHUTTERAMPLIFIER SPEED SETTING ALARM CIRCUIT ELECTRONIC FLASH o START TRIGGERMll/EA/TO/PS TOMOJ/ MUIPATA SADAO YAMAOKA May 28, 1974 TQMQJ] MURATAETAL Re. 28,025

AUTOMATIC CONTROL DEVICE FOR ELECTRONIC FLASH Original Filed April 18,1968 11 Sheets-Sheet 5 FIG.?

SWITCH CIRCUIT START TRIGGER L l/VVE/V TORS TOMOJ/ MU/PATA S4040 MMAO/(Awn e May 28, 1974 TOMOJI MURATA ETAL Re. 28,025

AUTOIATIC CONTROL DEVICE FOR ELECTRONIC FLASH Original Filed April 18,1968 11 Sheets-Sheet 6 L r ,i Km I 5:- oTo COMPARATOR a J "Ru .0:

lzii TRIGGER TO OUTPUT WINDING OF 3 CIRCUIT I Z: BLOCKING TRANSFORMER T.

-H- C7 CG'T' F t R \1 R13 '4 L N INVENTO/PS TOMOJ/ Mil/P474 5140/40YAMAOKA Z y FL H y 1974 TOMOJI MuRATA ETAL Re; 28,025

AUTOIIAT I C CONTROL DEV I C E FOR ELECTRONI C FLAS H Original. FiledApril 18, 1968 ll Sheets-Sheet '7 FIG.|O

FEEDBACK ELEMENT FOR FLASH LIGHT INTEGRATIoN NATURAL AND FLASH LIGHTFILM SENSITIVITY SETTING (LENs APERTURE CONPARATOR sETTI NG) i- 9 A B P0G LIGHT LENs APERTURE AMPLIFIER MEASURING sETTING PORTION IoR FILMSENSITIVITY SETTING) FEEDBACK ELEMENT swITcI-I FOR NATURAL LIGHTOPERATION (SHUTTER SPEED SETTING) ELEcTRoNIc FLASH LIGHT ELEcTRoNIcFLASH +E +EI P g KIJLIII I zI.T

CI P R3 I I I. I

R2 R2 RI RI I/VI/ENTORS TOMOJ/ Mil/B474 $40140 YAMAOKA May 28, 1974TOMOJI M R T ETAL Re. 28,025

AUTOIATIC CONTROL DEVICE FOR ELECTRONIC FLASH Original Filed April 18,1968 11 Sheets-Sheet 8 FIG.I3

P CI 6 I4|------ F I G .l 4

NATURAL AND FLASH LIGHT D iiRs Ib R 7 SWITCHING CIRCUIT 2 START TRIGGERH II INVENTORS TOMOJ/ MU/PA 74 540/40 YAMAO/(A y 23, 1974 TOMOJI MURATAETAL Re. 28,025

AUTQHATIC CONTROL DEVICE FOR ELECTRONIC FLASH 11 Sheets-Sheet 9 OriginalFiled April 18, 1968 T FlG.l5

TO SWITCHING CIRCUIT FIGJG EERB FLASH LIGHT NATURAL LIGHT INVENTORSTOMOJ/ MU/MTA 540140 MMAO/(A 8) z :2

23, 1974 TOMOJI MURATA ETAL Re. 28,025

AUTOATIC CONTROL DEVICE FOR ELECTRONIC FLASH Original Filed April 18,1968 11 Sheets-Sheet 10 S F J l TRiGGEn TRIGGER 1 WW INPUT R| R6 F SCRZx R3 SCRZ R7 TRIGGER DELAY D s CIRCUIT c. i: 6 i341 Ce 4 s I T L 03 R5Re T R INVENTO/PS TOMOJ/ YAMAOKA SAD/10 YAMAO/(A May 28, 1,14 TQMQJlMURATA ETAL Re. 28,025

AUTOIATIC CONTROL DEVICE FOR ELECTRONIC FLASH Original Filed April 18,1968 11 Sheets-Sheet 11 START OF ELECTRONIC FLASH DISCHARGE ELECTRONICFLASH DISCHARGE OF CHARGE IN c. TURNED OFF TIMEr GATE INVERSE BIASSCR'ON SCRIOFF b C 0/6 1- l INVERSE VOLTAGE/ 1 TOMOJ/ MMAOKA 5340 40YAMAOKA United States Patent Office Reissued May 28, 1974 28,025AUTOMATIC CONTROL DEVICE FOR ELECTRONIC FLASH Tomoji Murata, 2306Kanaoka-chou, Sakai, Osaka, Japan,

and Sadao Yamaoka, 33-2 Nakanogawa-chon, Toyokawa, Aichi, Japan OriginalNo. 3,591,829, dated July 6, 1971, Ser. No. 722,287, Apr. 18, 1968.Application for reissue Apr. 11, 1972, Ser. No. 243,095

Claims priority, application Japan, Apr. 20, 1967, 42/25,:551; June 27,1967, 42/41,126; Aug. 7, 1967, 42/50,649; Aug. 21, 1967, 42/513,637 Int.Cl. 1101i 39/12; H05b 41/36 US. Cl. 315-151 19 Claims Matter enclosed inheavy brackets II] appears in the original patent but forms no part ofthis reissue specification; matter printed in italics indicates theadditions made by reissue.

ABSTRACT OF THE DISCLOSURE A device for automatic control of thequantity of light from an electronic flash, by comparing the brightnessof a photographic object with the quantity of light required forparticular photographing conditions including the degree of lensaperture selected and the sensitivity of the film used. The brightnessof the photographic object is measured as the sum of the natural lightbrightness and the brightness due to electronic flash, and as soon asthe sum brightness thus measured reaches the required quantity of light,a stop signal is given. Thereby, the electronic flash is controlled, andat the same time signal is given for the suflicient brightness of thephotographic object.

This invention relates to a device for automatic control of the quantityof light from electronic flash, responsive to the brightness of therespective photographic object in view of settings of the sensitivity offilm, the degree of lens aperture, and shutter speed. More particularly,the present invention relates to an automatic controlling device for thequantity of light from electronic flash, which is capable of electronicflash photographing with or without the daylight by measuring both thenatural or daylight component and the electronic flash component of thebrightness of the photographic object.

With known automatic devices for controlling the quantity of light, ithas been extremely diflicult to carry out electronic flash photographingin the daylight, because only the light beams from electronic flash ismeasured by a photoelectric means, for determining the quantity oflight, and hence, in measuring the brightness including the electronicflash light and natural light, there has been a considerably large errorfor the daylight brightness comparable with the electronic flashbrightness.

Therefore, an object of the present invention is to obviate suchdifliculty of the known devices for controlling the quantity of lightfor photographing by providing an automatic device for controlling thequantity of light from electronic flash and for giving an alarm for thedaylight sufl'icient for eliminating the need of electronic flash, whichdevice, for instance, includes two photoelectric elements to measure thebrightness of each photographic object in two separate quantities, i.e.,one due to daylight and another due to electronic flash, respectively,so that the actual brightness of the object can be achieved by addingthe above two quantities for regulating the quantity of light from theelectronic flash, as Well as for generating alarm signal in cases wherethe daylight is sufficient for successful photographing withoutnecessitating the use of the electronic flash.

Another object of the present invention is to provide an automaticdevice for controlling the quantity of light from the electronic flashand for giving an alarm when the daylight is bright enough to eliminatethe need of electronic flash. The device includes a photoelectricelement for measuring the overall brightness of each photographic objectowing to both the natural daylight and electronic flash; adiscriminating means adapted to separate the DC component of the outputfrom the photoelectric element, representative of the intensity ofslowly changing daylight component of the object brightness, from theremaining AC component of said photoelectric element output,representatiwe of the intensity of rapidly varying electronic flashcomponent thereof; an integrator-amplifier adapted to integrate the thusdiscriminated AC component to produce an output representing quantity oflight from the electronic flash and to amplify the DC component; anadder to add the thus integrated electronic flash component and thedaylight component so as to produce a brightness output; a referencemeans for producing a reference output representing the sum of settingson film sensitivity, degree of lens aperture, etc.; a comparator tocompare said brightness output with said reference output, so as toproduce a control output; a control means to regulate the quantity oflight from said electronic flash in response to said control output; andan alarm means for giving an alarm when said daylight quantity is toohigh to use said electronic flash.

A further object of the present invention is to provide a device forautomatically controlling the quantity of light from electronic flash,which device includes a photoelectric element adapted to determine theoverall brightness of each photographic object; an integrator adapted tointegrate AC component of the output from said photoelectronic element,representing rapidly varying electronic flash component of saidphotoelectric element output, and to amplify DC component of saidoutput, representing slowly varying daylight component thereof, so thatsaid integrator produces an integrated output representing the sum of aquantity proportional to the electronic flash light quantity and anotherquantity proportional to the daylight quantity as modified by a selectedshutter speed; a reference means for producing a reference outputrepresenting one or more settings on film sensitivity, degree of lensaperture, etc.; a comparator for comparing said integrated output andsaid reference output to produce a control output; and a control meansfor controlling the quantity of light from said electronic flash,responsive to said control output.

Another object of the present invention is to provide an automaticdevice for controlling the quantity of light from the electronic flashof any of the aforesaid types, which device includes a switch circuitconsisting of SCR switch elements for regulating said quantity of lightfrom electronic flash, having a starting unit and a bias unit forproviding reverse bias to quicken the turnoff operation thereof.According to the present invention, the switch circuit is connected inseries with the electronic flash, so that the duration of lightemanating from the electronic flash can be controlled by regulating theswitching time of said switch circuit. To insure satisfactory operationat high speed, the switch circuit should have a high interruptingcapacity to deal with the high loss during such high speed switchingoperation. 0n the other hand, as well known to those skilled in the art,the instantaneous peak current in an SCR can be several ten times aslarge as the maximum mean forward current, and in the case of electronicflash circuit, the duration of current flowing through the SCR, if used,is very short with comparatively long nonconducting periods betweensucceeding operations. Accordingly, a small capacity SCR can be used inthe electronic flash circuit. Since the small capacity SCR hasdifliculty in turning olf a large current, in the device of theinvention,

a counterbias means is provided to shorten the switching time down totwo-thirdsone-third of that without it.

Other objects and a fuller understanding of the present invention may behad by referring to the following description, taken in conjunction withthe accompanying drawings, in which:

FIG. I is a block diagram of a control device embodying the presentinvention;

FIG. 2 is a circuit diagram of the control device;

FIG. 3 is a circuit diagram of a switch circuit with an alarm means,usable in the control device;

FIG. 4 is a simplified circuit diagram of a means for measuring thequantity of light of daylight or natural light brightness;

FIG. 5 is a schematic diagram of a circuit for setting the filmsensitivity, the degree of lens aperture, and the like;

FIG. 6 is a block diagram similar to FIG. 1 but showing another controldevice according to the present invention;

FIG. 7 is a circuit diagram of the control device of FIG. 6;

FIGS. 8 and 9 are diagrams similar to FIGS. 5 and 3 respectively butshowing a setting circuit and a switch circuit usable in the device ofFIG. 6;

FIG. 10 is a block diagram of another embodiment of the presentinvention;

FIG. 11 is a circuit diagram of a computing means for electronic flashlight;

FIG. 12 is a circuit diagram of another computing means for daylight ornatural light;

FIG. 13 is a circuit diagram of an integrator of quantity of light.actually used in the device of FIG. 10;

FIGS. 14 and 15 are circuit diagrams of the device of FIG. 10;

FIG. 16 is a circuit diagram of a diflerent light measuring means,usable in the control device according to the present invention;

FIG. 17 is a circuit diagram of switching means usable in any of theaforesaid control devices; and

FIG. 18 is a graph showing curves representing operation of variouscircuit elements in the device according to the present invention.

Like parts and elements are designated by like numerals and symbolsthroughout the drawings.

The quantity of light to be emanated from an electronic flash forsuccessful photographing is determined in the following manner, in thecontrol device according to the present invention. For the sake ofsimplicity, it is assumed in the following derivation of equations thatseparate photoelectronic elements are used for electronic flash lightand for daylight or natural light. However, it is apparent to thoseskilled in the art that by using a suitable discriminator means, thequantity of light for both the electronic flash and natural light can bedetermined with only one photoelectric element.

If the overall brightness of the photographic object is assumed to havea value B due to daylight or natural light and another value B due toelectronic flash light, then the quantity of light delivered to aphotoelectric element P for electronic flash is equal to K (B +B K beinga constant. Accordingly, the total output current from the photoelectricelement P is wherein K is another constant,

i is a photoelectric current generated by light from the electronicflash, and

i is a photoelectric current generated by natural light. Thephotoelectric current i generated by natural light can be considered asa direct current, because the natural light intensity varies only veryslowly. Hence, by passing the output current from the photoelectricelement P, through an AC amplifier, the DC component i thereof can beeliminated, so as to produce an amplified AC component K i K being aconstant. By integrating the thus separated AC component for the timeperiod corre sponding to each energization of the electronic flash, thefollowing output can be achieved.

K, I i dt (K being a constant) 0n the other hand, another photoelectricelement P for natural light has the same output (i,+i,,) as that of thepreceding element P Upon bypassing the AC component, by means of acapacitor, the DC component, representing the brightness due to thenatural light, can be separated and delivered as an output quantity K i(K being a constant).

It is apparent to those skilled in the art that by using a suitablecombination of high-pass and low-pass filters, the aforesaid twophotoelectric elements P, and P can be replaced with only onephotoelectric element P, to achieve the same output quantities K fi dtand K i The proper quantity of light to he expressed to a film isgenerally given by the following equation.

(I B dt+B T) /F =K/S Here,

F represents the degree of lens aperture, T the shutter speed selected,

S the sensitivity of the film used, and

K a constant.

Accordingly, the following relation should be satisfied for successfulphotographing.

The last mentioned equation gives the quantity of light to be generatedby an electronic flash for successful photographing.

Now, referring to FIG. I, the AC component of the output from aphotoelectric element P for detecting light from an electronic flash isamplified by an AC amplifier for separating the DC component thereof andfor amplifying the AC component. Then the AC component is integrated byan integrator to deliver an output quantity proportional only to themagnitude of the AC component. On the other hand, the AC component ofthe output from another photoelectric element P for detecting naturallight is bypassed by a suitable capacitor, so that the remaining DCcomponent of the output from P is delivered as another output quantity BT, incorporating the shutter speed setting. The two output quantitiesare added by an adder to produce a brightness output A, which is appliedto a comparator.

Another input quantity to the comparator is an output B, which is equalto KF /S and represents the settings of the degree of lens aperture andthe film sensitivity, as defined above.

If the quantity of light from the electronic flash increases to raisethe level of the brightness output A delivered to the comparator, untilit coincides with the setting output B representing the film sensitivityand the degree of lens aperture, then the condition of A=B is achievedand a stop signal is delivered to a switch circuit to turn it off.Thereby, proper quantity of light for the given setting can be achieved.

If there is a very strong natural light available, which is sufficientfor successful photographing without energizing the electronic flash,for a given shutter speed T, then the condition of AZB is established,so that the comparator generates a stop signal before energization ofthe electronic alarm, to actuate the alarm circuit. Thereby, the alarmis given to notify that the electronic flash need not be energized.

In FIG. 2, the output from the photoelectric element P, for detectinglight from the electronic flash is connected to an AC amplifier, whichconsists of a transistor Q resistors R R R R capacitors C and C Theoutput from the AC amplifier is applied to an integrator comprising afield effect transistor Q resistors R R R R capacitors C and C Anelectric quantity, repre sentative of the quantity of natural light, canbe produced by a circuit including a photoelectric element P atransistor Q resistors R R R and a capacitor C A Zener diode D isconnected to the base of the transistor Q, to maintain the base voltageat a constant level E The shutter speed setting is represented byregulating the resistance value of the resistor R which is a rheostattype. By connecting, in series, the resistor R of the integratorassociated with the electronic flash to the resistor R associated withthe natural light, the brightness output A can be produced.

FIG. 4 shows the details of the natural light detecting circuit of anadder circuit, in which a constant standard voltage E, is applied acrossthe base of the transistor Q having the photoelectric element Pconnected to the emitter thereof. Then, the differential voltage betweenthe base and the emitter of the transistor is small, and a substantiallyconstant voltage E is applied across the photoelectric element Pregardless of the resistance variation of the element P,,. If thephotoelectric element P has the performance characteristics K/B,, R,wherein K is a constant, B is the brightness at the element, and R isthe internal resistance of the element, then the emitter current i canbe given by i,,=E /R:E,,B,,/K". In this case, the collector current i,,is approximately the same as the emitter current i namely i C ei If theresistance value of the variable resistor R is so adjusted as torepresent the shutter speed T according to the relation of then thevoltage across the resistor R represents the quantity of light clue tonatural light, which is given by If the resistance value of R isselected to be very large, as compared with R or R R then only R acts asthe efl'ective load resistor of the integrator and R becomes negligibleas the load resistor. Thus, the voltage across the resistor R is givenby fi fi dt, which represents the quantity of light of the electronicflash. Accordingly, the brightness output terminals across the resistorsR and R receive a voltage given by Referring back to FIG. 2, acomparator is connected to the brightness output terminals through ablocking transformer T which comparator comprises a transistor Q acapacitor C and variable resistors R R for setting the film sensitivityand the degree of lens aperture. In FIG. 5, if the resistor R is assumedto be not acting as a load of the resistor R then the output voltageacross the slider of the resistor R is determined by the position ofeach slider of the resistors R and R By adjusting the sliders of thelinearly variable resistors R and R it is possible to produce a settingoutput KR /S at the output terminal, which is the slider of the resistorR In FIG. 2, a capacitor C is charged with the setting output voltage,and the voltage across the capacitor C is continuously compared with thebrightness output voltage, appearing across the resistors R and Rconnected in series, which varies according to the formula (K ji dt-t-Ki T) When the brightness output voltage across the resistors R and Rbecomes the same as the setting voltage across the capacitor C thetransistor Q of the comparator is blocked, so that a stop signal pulseis generated at the output winding of the transformer T which is thendelivered to a switch circuit.

Cir

FIG. 3 shows the construction of the switch circuit for clamping theelectronic flash L. When a start switch SW of the electronic flash isclosed, the electronic flash L is actuated, and at the same time, atrigger circuit actuates the trigger SCR to bring it into conductivestate. Upon application of the stop signal pulse from the transformer Tto an SCR of the switch circuit, the SCR becomes conductive to bypassthe current of the electronic flash L through a capacitor C Thus, theSCR becomes nonconductive, and when the capacitor C is charged in thereverse direction, the electronic flash L is turned off. Thus, thedesired quantity of light is obtained from the electronic flash L.

There is provided an alarm neon tube N across a resistor R throughanother resistor R If the quantity of natural light is suflicient forphotographing, or if the brightness output exceeds the setting outputrepresenting the film sensitivity S and the degree F of the lensaperture, without actuating the electronic flash L, the comparatorgenerates the stop signal pulse continuously, to make the SCRconductive. The resistance value of the resistors R and R is selected tobe high enough not to maintain the SCR conductive when the stop signalpulse is removed. Thus, the SCR becomes conductive only when the stopsignal pulse is applied thereto. In other words, the voltage isintermittently applied across the resistor R to flash the neon tube N.As a result, the flashing of the neon tube N gives an alarm informingthat the electronic flash L need not be actuated.

As described in the foregoing, according to the present invention, thenatural light component and the electronic flash light component of thebrightness of the photographic object are measured separately, so thataccurate exposure control can be insured. On the other hand, knownexposure control systems for electronic flash photographing measure onlythe electronic flash component of the brightness even in daylight.Moreover, when the daylight is sufficient for particular photographingconditions, the alarm signal is given to indicate that the electronicflash need not be actuated, so that proper application of the electronicflash is insured.

Referring to FIG. 6, illustrating the block diagram of anotherembodiment of the present invention, a portion of the output from aphotoelectric element P is applied to a high-pass filter HPF and thenintegrated by an integrator, to produce an integrator output, which isproportionate only to the quantity of light from an electronic flash.The remaining portion of the Output from the photoelectric element P isapplied to a low-pass filter LPF and then amplified by a DC amplifier,to produce an amplifier output through a means for setting shutterspeed. The output from the shutter speed setting means represents aquantity B T which is proportionate only to the quantity of naturallight. An adder is provided to take the sum A of the integrator outputand the shutter speed setting means output, so as to apply the thusachieved sum to a comparator. The sum A corresponds to the brightnessoutput of the preceding embodiment, described in detail hereinbeforereferring to FIGS. 1 to 5.

A setting output 13, which represents a quantity KF /S, indicative ofthe film sensitivity and the degree of lens aperture is applied to thecomparator, so that the setting output B may be compared with thebrightness output A, in the same manner as in the preceding embodiment.

In FIG. 7 showing the circuitry of the device of FIG. 6, the output fromthe photoelectric element P is taken as the voltage across a resistor Rconnected in series to the element P. A high-pass filter HPF consists ofa capacitor C and a resistor R An integrator is formed by a field effecttransistor Q resistors R R R R and capacitors C C A Zener diode D isused to maintain the bias voltage of the field transistor Q, at aconstant level. A resistor R and a capacitor C constitute the lowpassfilter LPF, while a transistor Q and resistors R R form the detector ofnatural light. The resistor R is of rheostat type and acts as a meansfor setting the shutter speed indication, and the series connection ofthe resistors R and R contributes to produce the sum of the electronicflash light component and the natural light component of thephotographic object brightness, i.e. a brightness output A.

To determine the natural light component of the brightness the resistorR connected in series to the transistor Q has a high resistance value,so that it does not act as the load of the low pass filter. Then, thevoltage across the resistor R is approximately the same as the outputvoltage from the low-pass filter. If the resistance value R of thephotoelectric element P has the characteristics of Ral/B wherein B isthe brightness at the photographic element, the emitter voltage E isgiven by the following equation.

E, represents the voltage applied to the photoelectric element, and

R represents the resistance value of the resistor R which is negligiblysmall, as compared with R, i.e. R R.

In this case, the collector current is about the same as the emittercurrent, and hence, the collector current i can be given by thefollowing equation.

If the shutter speed T is so selected as to establish R =K T, wherein Ris the resistance value of the variable resistor connected in series tothe transistor Q then the voltage across the resistor R is given by Ki':K i,,T=K'B T (K being a constant).

The above voltage across R represents the quantity of natural light.

If the resistance value of R is selected to be for larger than R so asto establish the relation of R R then the resistor R acts as the loadresistor of the integrator, while R becomes negligible as the load ofthe integrator. Thus, the voltage across R becomes K ji dt representingthe quantity of light from the electronic flash. Accordingly, the outputvoltage across the resistors R and R connected in series becomes (K. J'idt+K i T), which is the brightness output.

In FIG. 7, a comparator comprises a transistor Q a capacitor C and ablocking transformer T The film sensitivity and the degree of lensaperture are set by regulating the sliders on the resistors R and Rrespectively.

The circuitry for setting the film sensitivity and the lens aperturedegree is shown in FIG. 8. If the resistor R is assumed not to act as aload of the resistor R the output from the resistor R is determined bythe position of sliders of each resistor. If the sliders of the linearlyvariable resistors R and R are so set as to represent K/S and Frespectively, then the output from the resistor R represents thefunction KF /S, or the setting output, as in the case of the precedingembodiment.

A capacitor C is provided to store the setting output KF /S from theresistor R as a voltage across the capacitor. The brightness output (Kdidt- K io l, appearing across the resistors R and R connected in series,is compared with the aforesaid setting output KF KS, stored in thecapacitor C so that if the two outputs coincide, the comparator isblocked and produces a stop signal pulse at the secondary differentialwinding of the transformer T The stop signal pulse actuates the switchcircuit.

In FIG. 9, when an electronic flash starting switch SW is closed, theelectronic flash L is energized, and at the same time, the triggercircuit is actuated to make a silicon controlled rectifier SCR,conductive. If the stop pulse signal from the comparator, indicating thecoincidence of the setting and brightness outputs, is delivered toanother silicon controlled rectifier SCR- and the current in theelectronic flash L is shifted to a path through a capacitor C and SCRand hence the SOR, is blocked. Accordingly, as the capacitor C ischarged in the opposite polarity, the electronic flash L is deenergized.Thus, the quantity of light from the electronic flash is controlled, bystopping it at any desired moment.

A neon tube N is connected across a resistor R through another resistorR for alarm purpose. When the brightness output reaches the same levelas the setting output without energizing the electronic flash, or whenthe natural light is suflicient for the desired photographing withoutactuating the electronic flash, the stop signal pulse is continuouslydelivered from the comparator to the SCR In this case, due to the highresistance value of the resistors R and R the SCR cannot remainconductive after the stop signal pulse is removed. In other words, theS011 is conductive only when the stop signal pulse is applied thereto.Thus, an intermittent voltage is applied across the resistor R to ignitethe neon tube N. As a result, the flashing of the neon tube N indicatesthat the electronic flash need not be energized.

As described in the foregoing, according to the present invention, boththe natural light component and flash light component of the brightnessof the photographic object can be detected by a single photoelectricelement, and then the output from the photoelectric element is dividedinto the flash component and natural light component the lattercomponent, incorporating the shutter speed setting, so that the exposureto the electronic flash can be controlled more accurately than by anyknown automatic methods of measuring only the flash light quantity.Moreover, when the natural light is sufficient for satisfactoryphotographing under certain photographing conditions, an alarm is givento indicate that the electronic flash need not be energized. Thus,successful flash photographing is insured with and without daylight.

FIG. 10 shows a block diagram of another embodiment of the presentinvention, in which an integrator capable of both integration and simpleamplification is used. A photoelectric element in the light measuringportion receives light from the photographic object, including thenatural light and flash light components. The output current from thephotoelectric element is modified by the setting of the sensitivity ofthe film used or lens aperture degree selected, and then applied to anintegrator at the amplifier portion thereof. The AC component of theoutput from the amplifier is fed back to its input side through afeedback element for integration of the flash light component, while theDC component of said output is fed back to the input side of theamplifier through another feedback element for natural light. Thus, atthe output side of the amplifier, an output representing the quantity offlash light is provided. At the same time, another output representingthe quantity of natural light, as modified by the aforesaid setting isalso delivered to the output side of the amplifier. The two outputquantities are added to form a brightness output A, representing boththe natural light and the flash light components of the objectbrightness, which is then applied to a comparator. A setting output B,representing the film sensitivity or the degree of lens aperture, isalso applied to the comparator, so as to be made reference to thebrightness output A. When the quantity of light from the object isincreased by the electronic flash, until the brightness output Acoincides with the setting output B, a stop signal pulse is generated atthe comparator, which is then dispatched to a switch circuit, to turn itoff. Thus, the quantity of light from the electronic flash is controlledat a desired level. In the illustrated embodiment, the degree of lensaperture or the sensitivity of film used is incorporated in the lightmeasuring portion on one side of the comparator. How ever, it is alsopossible to incorporate both the lens aperture setting and the filmsensitivity setting in the setting output B to be applied to thecomparator from the opposite end thereof.

FIG. 11 illusrates a circuit for integrating the electronic flash light.The voltage e, across a resistor R produced by an electric current ifrom the photoelectric element P and representing the quantity of theelectronic flash light, is given by A capacitor C and a resistor Rconstitute an integrator for integrating the quantity of the electronicflash light, which delivers the integrated value as a voltage E across aresistor R FIG. 12 shows a circuit for computing natural light quantity,in which the voltage e across a resistor R produced by an electriccurrent i from the photoelectric element and representing the naturallight quantity, is given y It is fed back through another resistor fornatural light feedback. Accordingly, the DC output voltage E is given asfollows.

Here,

K voltage gain, without feedback 3: feedback ratio, fl=R /R Assumingthat 1/K is negligible as compared with e, i.e. 18 l/K the DC output canbe given by Thus, the amplification factor of this circuit becomes K /RBy setting the quantity 1/R as the shutter speed setting value T, oneobtains E K i T.

FIG. 13 shows a circuit to be used for integrating and amplifying thequantity of light, from each photographic object, in which the circuitsof FIGS. 11 and 12 are incorporated. A capacitor C is connected inparallel with the resistor R is for bypassing the AC component to theground, so as to prevent the AC component from being fed back. Thus,only the DC component is fed back for synthesis. The voltage E acrossthe resistor R represents the sum of the DC output E and AC output Ewhich sum can be given by On the other hand, the proper quantity oflight at the film surface is given by (l/F (J'B dt+B T) =K/S wherein,

B, represents the brightness of the photographic object,

due to the electronic flash,

B the brightness of the same, due to natural light,

F the degree of lens aperture,

T the shutter speed,

S the film sensitivity, and

K a constant.

By rearranging,

It K, and K are so chosen as to satisfy the relations of B =K i andB,,=K i then the equation (1) can be equated with the equation 2).

Thus, the output voltage E can be given by The last mentioned equationrepresents the quantity of light to be emanated by the electronic fiash.

By rearranging the equation (3),

1.r s 2 o (K,fi dt+K i T) /F =K/S (5) FIGS. 14 and 15 show circuitryembodying the present invention. In FIG. 14, a load resistor R, isconnected in series with the photoelectric element P to deliver anoutput voltage proportional to the magnitude of the output current fromthe photoelectric element. A field transistor Q resistors R R R R andcapacitors C C2 constitute an integrator for the quantity of light.Resistors R and R act to provide the bias voltage to the fieldtransistor Q under the conditions that the current flowing through theresistors R and R is sufliciently large, as compared with the currentthrough the field transistor Q. A capacitor C serves to bypass the ACcomponent of the output current from the photoelectric element, so thatthe AC component is not fed back. By properly selecting the values ofresistors R R and the capacitor C,, an integral K fi dt can be achieved,which represents the quantity of light from the electronic flash. Thevariable resistor R serves for setting the shutter speed, and the outputvoltage K i T can represent the quantity of natu ral light if the valuesof resistors R R and R are properly selected. As a result, the voltageacross the resistor R gives the following sum.

A comparator in this embodiment comprises a transistor Q a capacitor C;and a blocking transformer T while the variable resistors R and R arefor setting the film sensitivity and the degree of lens aperture,respectively. If the resistors R and R are so selected as to representthe linear functions K/S and F by properly positioning the sliders,respectively, then the output voltage from the resistor R can representa function KF /S corresponding to the thus selected positions of thesliders of the two variable resistors. A capacitor C is provided forstoring the output voltage KF S, generated at the variable resistor RWhen the output voltage at the resistor R which is given by (K ji dt-l-Ki T) increases and coincides with the voltage across the capacitor Cwhich is KF /S, then the comparator is blocked. Then, the output windingof the blocking transformer T generates a stop signal pulse, which isdelivered to a switch circuit to turn it off. Thus, the electronic flashis deenergized, so as to attain a desired quantity of light therefrom.

In the circuit of FIG. 15, the resistance of a resistor R in series withthe photoelectric element P is made variable in order to representeither the film sensitivity S or the lens aperture degree F. In otherwords, either one of S and F of the right hand side term KF /S of theequation (3), which is given as the voltage across the capacitor C inthe circuit of FIG. 14, is now shifted, so that the capacitor C of FIG.15 will store the righthand side term of the equations (4) or (5), i.e.K1 or K/S.

Table 1 shows the manner in which the shutter speed T, film sensitivityS and the lens aperture degree F are set according to the equations (3),(4), and (5), respectively in the embodiment.

TABLE 1 Setting method Voltage (equation) Bi Rt Output voltage of R; R1Rs R10 across C;

1(a) Fixed, Kiftdwmar if; F Ki /s II (3) do KifisdH-KaioT F g KF /S m(4) s stmfmwmm 1m rm 1 1 1 K K IV (5) T ,,(K1f1s l+R 110T) E 3 FIG. 16illustrates another circuit usable for measuring the light, which has apair of separate elements for detecting the natural light and theelectronic flash light, respectively. This detecting circuit can bereplaced with that portion of the circuit of FIG. 14 or 15, which is tothe left of the chain line thereof. An element having a P-N junctionwith the photoelectric effect, such as a photocell, a solar batterycell, or a phototransistor, can be used for each or either one of thedetecting elements, so as to prevent interference between the twodetecting elements by using a reverse bias by taking advantage of therectifying charactristics of such P-N junction elements. At the sametime, it is made easier to achieve linear relations between the outputcurrent and the natural light or electronic flash light.

As described in the foregoing, according to the present invention, alight quantity integrating circuit is provided, which is adapted tointegrate the AC component of the light quantity, i.e. the electronicflash light component thereof, and to merely amplify the DC. component,i.e. the natural light component. Moreover, the amplification factor ofthe integrator can be varied regardless of the integrating functionthereof for the AC component. With such characteristics of theintegrator, it is made possible to vary the shutter speed in accordancewith the amplification factor, so that the natural light quantity can beeasily measured. The fact that the output of the integrator is the sumof the quantities of the natural light and the electronic flash light isparticularly advantageous for the control purposes. In this integrator,the setting of the film sensitivity and the degree of lens aperture canbe carried out by adjusting the output from the light detectingelements. Furthermore, the sensitivity of the light detecting elementscan be easily adjusted, because the integrating and amplifying functionsof the integrator are independent with each other, even when thesensitivities of separate light detecting elements for the natural andelectronic flash light are modified separately.

FIG. 17 shows a switch circuit usable in the control device according tothe present invention and FIG. 18 shows the operating characteristics ofsuch a switch circuit. The turnoff section of the switch circuitincludes a pair of silicon controlled rectifiers SCR and SCR The SCRfacilil tates the commutation of the SCR When a switch SW is closed toactuate a high voltage trigger transformer T, a high voltage pulse isdelivered to an actuating electrode of the electronic flash L, so as tostart the electronic flash L by discharging a capacitor C connected inparallel with the electronic flash L. When the voltage across thecapacitor C drops as it discharges, an electric current flows through acircuit including a capacitor C a diode D and a resistor R and reachesthe gate of the SCR as a positive gate current. Thus, the SCR is madeconductive. Hence, the electronic flash L is maintained as energized.Such starting operation is illustrated in FIG. 18.

The turn-offoperation of the switch circuit will now be described.Before the SCR, is turned off, a capacitor C is charged throughresistors R and R in the polarity as shown in FIG. 17. Another capacitorC is also charged through resistors R R R R A trigger delay circuit isactuated as soon as the switch 5 is closed, to generate a dclayed pulse.When this delayed pulse is applied to the gate of the SCR to make itconductive, the capacitor C is discharged, so that a reverse currentflows through the SCR to turn it off. At the same time, with the SCRmade conductive, the charge in the capacitor C is discharged throughresistors R R and the diode D to apply a reverse bias to the SCR Thetiming of the application of such reverse bias is determined by thecapacity of the discharge circuit of capacitor C and the time constantof the resistors therein, and the reverse bias is applied to the SCReven after the application of starting voltage is initiated. Thus, thedu/dt characteristics are improved and the turnoff time is shortened.Accordingly, the conductive period of the SCR which is necessary to turnoff the SCR can be also shortened, and hence, the current carryingcapacity of SCR can be small.

Behaviors of various currents and voltages during this turnoff operationare depicted in the curves of FIG. 18. When the commutation capacitor Cis charged to the power source voltage E, the current through the SCR isinterrupted, and the SCR itself is blocked. A resistor R is provided tofacilitate the discharge of the capacitor C while the resistor R is torecharge the capacitor C in the polarity as shown in FIG. 17, after theelectronic flash L is turned off.

As described in the foregoing, according to the present invention, thereis provided a switch circuit to be closed upon firing of the electronicflash, which has a simpler circuit construction than that of any knownswitching circuit including a trigger circuit to be triggered to makethe switch circuit conductive. With the shortened turnoff time, thesilicon controlled rectifiers to be used in this switch circuit can beof a very inexpensive type, and hence the switching circuit can be madeat low cost.

Although the present invention has been described with a certain degreeof particularity, it is understood that the present disclosure has beenmade only by way of example and that numerous changes or modificationsin the details of construction and the combination and arrangement ofparts may be resorted to without departing from the spirit and the scopeof the invention as hereinafter claimed.

We claim:

1. An automatic control circuit for determining the duration of lightemitted by an electronic flash unit, said control circuit comprisingphotoelectric means positioned to receive light reflected from an objectilluminated by natural light and by flash light from the electronicflash unit, electric filter means coupled to said photoelectric meansand operative to furnish at a first output thereof a first componentrepresentative of the reflected natural light and at a second outputthereof a second component representative of the reflected flash light,integrating circuit means coupled to the second output of said electricfilter means for integrating said second component, an adding circuitcoupled to said integrating circuit means and to the first output ofsaid electric filter means and operative to produce an output voltageproportional to the sum of said first component and the integration ofsaid second component, circuit means to provide a reference voltageproportional to the exposure as established by the sensitivity of thefilm in the associated camera and the size of the lens aperture, acomparator coupled to said adding 13 circuit and to said circuit meansand operative to produce a control signal when the difference betweensaid output voltage and said reference voltage reaches a predeterminedvalue, and a firing circuit coupled to said comparator and to theelectronic flash unit for terminating the flash produced thereby uponreception of said control signal.

2. The automatic control circuit set forth in claim 1, wherein saidphotoelectric means includes a first photoelectric element and a secondphotoelectric element, and said electric filter means includes first andsecond filter portions respectively coupled to said first and secondphotoelectric elements, said first filter portion being operative topass only said first component and said second filter portion beingoperative to pass only said second component.

3. The automatic control circuit set forth in claim 1, wherein saidphotoelectric means consists of a single photoelectric element.

4. The automatic control circuit set forth in claim 1, wherein saidfiring circuit includes a capacitor coupled in parallel with saidelectronic flash unit and operative to fire said electronic flash unitby discharging therethrough, a starting section having a siliconcontrolled rectifier coupled to said capacitor and being conductive inresponse to the discharge of said capacitor to close a switchablecircuit through the electronic flash unit, a reverse bias section forapplying a reverse bias to said silicon controlled rectifier uponreapplication with a predetermined time delay determined by a capacityand a resistance, and a pair of diodes preventing mutual interferencebetween said starting section and said reverse bias section.

5. The automatic control circuit set forth in claim 1, and furthercomprising an indicating means coupled to said comparator and beingoperative to provide an alerting signal when said output voltage exceedssaid reference voltage.

6. An automatically controlled flash illuminating network comprisingmeans including a photosensitive element for producing a control signalin response to a predetermined amount of light incident on saidphotosensitive element, a storage capacitor, a first semiconductorswitching device including a control electrode and two main currentcarrying electrodes, a flash tube coupled in series with said firstsemiconductor switching device, said series circuit comprising saidfirst semiconductor switching device and said flash tube being connectedin parallel to said storage capacitor, means for firing said flash tubeand applying a closing trigger signal to the control electrode of saidfirst semiconductor switching device, a commutation capacitor. means forcharging said commutation capacitor, a second semiconductor switchingdevice including a control electrode and two main current carryingelectrodes, said device being actuatable to a closed condition inresponse to said control signal and coupled in series with saidcommutation capacitor ocross the main electrodes of said firstsemiconductor switching device whereby to apply a reverse voltagebetween said first semiconductor switching device main electrodes toopen said first semiconductor switching device in response to the saidclosing of the said second semiconductor switching device.

7. The network of claim 6 including means for applying a reverse bias tothe control electrode of said first semiconductor switching device inresponse to the closing of said second semiconductor switching device.

8. The network of claim 7 wherein said means for applying a reverse biascomprises a reverse biasing capacitor and impedance means series coupledbetween a main electrode of said second semiconductor switching deviceand the control electrode of said first semiconductor switching device.

9. The network of claim 8 wherein said impedance means comprisesresistor means.

10. The network of claim 6 wherein said means for applying a closingtrigger signal to said first semiconductor switching device includesimpedance means connected with said flash tube and a control electrodeof said first semiconductor switching device for causing a closingtrigger signal to be applied to said control electrode of said firstsemiconductor switching device in response to the firing of said flashtube.

11. The network of claim 10 wherein said impedance means comprises animpedance element and a capacitor element connected in series acrosssaid storage capacitor, said capacitor element being connected acrosssaid flash tube.

12. The network of claim I] wherein said impedance comprises at leastone resistor.

13. An automatically controlled flash illuminating network comprising astorage capacitor, a first semiconduo tor switching device including acontrol electrode and two main current carrying electrodes, anelectronic flash tube connected in series with said first semiconductorswitching device, said series circuit comprising said firstsemiconductor switching device and said flash tube being connected inparallel to said storage capacitor, means includ ing a photosensitiveelement for producing a control signal in response to a predeterminedamount of light incident on said photosensitive element, a secondsemiconductor switching device including a control electrode and twomain current carrying electrodes octuatable to a closed condition inresponse to said control signal, means including a commutation capacitorinterconnecting corresponding main electrodes of said first and secondsemiconductor switching devices, means connecting said commutationcapacitor across said storage capacitor whereby the closing of saidsecond semiconductor switching device applies the voltage of saidcommutation capacitor as a reverse voltage across said firstsemiconductor switching device, means responsive to the closing of saidsecond semiconductor switching device for applying a reverse bias to thecontrol electrode of said first semiconductor switching device andincluding a capacitor coupled between the control electrode of Saidfirst semiconductor switching device and a main electrode of said secondsemiconductor switching device, means for applying a closing triggersignal to the control electrode of said first semiconductor switchingdevice, including a capacitor shunting said flash tube and coupled tothe control electrode of said first semiconductor switching device, anddiode means coupled with said first semiconductor switching devicetrigger means and said means for applying a reverse bias.

14. The network of claim 13 wherein each of said semiconductor switchingdevices is a silicon controlled rectifier.

15. An automatically controlled flash illuminating network comprisingmeans including a photosensitive element for producing a control signalin response to a predetermined amount of light incident on saidphotosensitive element, a storage capacitor, a first switching deviceincluding a control electrode and two main current carrying electrodes,a flash tube coupled in series with said first switching device, saidseries circuit comprising said first switching device and said flashtube being connected in parallel to said storage capacitor, means forfiring said flash tube and applying a closing trigger signal to thecontrol electrode of said first switching device, a commutationcapacitor, means for charging said commutation capacitor, 11 secondsemiconductor switching device including a control electrode and twomain current carrying electrodes, said device being actuatable to aclosed condition in response to said control signal and coupled inseries with said commutation capacitor across the main electrodes ofsaid first switching device whereby to apply a reverse voltage betweensaid first switching device main electrodes to open said first switchingdevice in response to the said closing of the said second switchingdevice.

16. An automatically controlled flash illuminating network comprising aDC. voltage source, a switching device, an electronic flash tube forproducing light energy of extremely short duration, said flash tubebeing coupled in series with said switching device across said voltagesource, means for firing said flash tube and closing said switchingdevice, sensing means including photosensitive means for producing anelectrical signal which is a function of the total value of the lightincident on said photosensitive means, means including a commutationcapacitor connected to be charged by said network, and means responsiveto said sensing means at a predetermined value of said electrical signaland operable with said commutation capacitor to apply a reverse voltageto said switching device for opening said switching device in responseto a predetermined amount of light incident in said photosensitive meansto extinguish said flash tube thereby terminating light energy from saidflash tube.

17. A network as defined in claim l6 wherein the lastnamed meansincludes a second switching device actuatable to a closed condition whensaid electrical signal is at a predetermined value and coupled in serieswith said commutation capacitor and said first switching device wherebyto apply a reverse voltage across said first switching device to opensaid first switching device in response to the said closing of saidsecond switching device.

18. A network as defined in claim 17 wherein said D.C. voltage sourceincludes main storage capacitor means References Cited The followingreferences, cited by the Examiner, are of record in the patented file ofthis patent or the original patent.

UNITED STATES PATENTS 3,392,284 7/1968 Cain 323-22 SC 3,350,604 10/1967Erickson 3l5151 3,464,332 9/1969 Davison et a1. 9510 HERMAN KARLSAALBACH, Primary Examiner L. J. DAHL, Assistant Examiner US. Cl. X.R.

